Run Flat limits

[Pat68]

Originally Posted by Tomaz

ps, 2 cheap Malaysian tyres fitted and balanced were less than half the price of 1 Bridgestone !!!!!

Pat

What was the brand of those Malaysian tyres? Your tyres link didn't reveal. Just wondering. I am going to stick with Bridgstone when its time for a change.

Hi Tomaz,

The tyres are made by a company called Jinyu.

Eu ratings, wet economy noise (db) price each £/$

Jinyu C C 73 62/81
Bridgstone B E 73 250/328

A obviously the best, E the worst.

Like I said, a bit of an experiment

Pat

[Pat68]

Hi ard,

Thanks for the warning

Do you mean rolling circumference?

The static diameter of the new rear tyres is <1 cm greater than the fronts, which considering the fronts are part worn I think is quite close. That said, this gives a difference of 18mm (3/4") in the static circumference front to rear.

Do you know if there is an allowable difference/tolerance and if so what it Is?

Thanks Pat

[ard]

Originally Posted by Pat68

Hi ard,

Thanks for the warning

Do you mean rolling circumference?

The static diameter of the new rear tyres is <1 cm greater than the fronts, which considering the fronts are part worn I think is quite close. That said, this gives a difference of 18mm (3/4") in the static circumference front to rear.

Do you know if there is an allowable difference/tolerance and if so what it Is?

Thanks Pat

Technically it is 'rolling diameter' or 'rolling radius' (since the tire deflects when rolling it really isnt a perfect circle so there isnt a circumference per se, or the circumference just gets distorted and doesnt change.)

0.75 is WAY TOO MUCH.

The stock BMW tires allows up to a 1% variance. We actually dont know the actual specification, but certain BMW wheels from the factory come with (I think) 712 rev/mile on one axle and 720 on another 8/720=1%. Hence one might infer that if BMW ships cars with that mismatch, that the engineering allows at least 1% tolerance

Stock size is roughly 29.0"... 29.0 versus 29.75 is way more than 1% You are probably running 3 times the tolerance.

You are likely stressing, perhaps wearing and maybe overheating the diff.

[Tomaz]

Originally Posted by Pat68

Hi Tomaz,

The tyres are made by a company called Jinyu.

Eu ratings, wet economy noise (db) price each £/$

Jinyu C C 73 62/81
Bridgstone B E 73 250/328

A obviously the best, E the worst.

Like I said, a bit of an experiment

Pat

Thanks. Good luck and keep us informed.

[ard]

Great prices... you can probably get 25 tires per transfer case.

[Pat68]

Originally Posted by ard

Technically it is 'rolling diameter' or 'rolling radius' (since the tire deflects when rolling it really isnt a perfect circle so there isnt a circumference per se, or the circumference just gets distorted and doesnt change.)

0.75 is WAY TOO MUCH.

The stock BMW tires allows up to a 1% variance. We actually dont know the actual specification, but certain BMW wheels from the factory come with (I think) 712 rev/mile on one axle and 720 on another 8/720=1%. Hence one might infer that if BMW ships cars with that mismatch, that the engineering allows at least 1% tolerance

Stock size is roughly 29.0"... 29.0 versus 29.75 is way more than 1% You are probably running 3 times the tolerance.

You are likely stressing, perhaps wearing and maybe overheating the diff.

Hi ard,

Once again thanks for the info.

I think I may have confused the issue a bit, I quoted the circumference of the tires, not the diameter......

I work best in metric so will try to give best info possible, even though they are metric size tires on imperial rims ???!!!!

Fronts, 50.8cm (20") rim, 11cm tire height (×2) = 72.8cm diameter (new) - 0.8cm (wear) = 72cm.
Rears, 50.8cm (20") rim, 11.025 tire height (×2) = 72.85cm diameter

Total difference 0.85cm. Which I think works out around 1.1% so only just outside the BMW 1% spec.

If my maths or understanding of your info is incorrect, please correct me. It's been a long time since I left school and college

Pat